Ambient-air fabrication of high-performance thick-film organic solar cells enabled by solid additive engineering

Organic solar cells (OSCs) fabricated under ambient air are essential for scalable and low-cost production, however, their power conversion efficiencies (PCEs) remain much lower than those of devices processed in nitrogen atmospheres. Herein, we introduce a solid additive, 3,5-dichloroiodobenzene (DCIB), to enable efficient air-processed OSCs with 65% relative humidity. DCIB improves molecular packing in the active layer, reducing energetic disorder and thereby enhancing exciton diffusion, charge transport, and suppressing recombination. Benefiting from compact molecular packing, DCIB-treated PM6:L8-BO-based OSC achieved an PCE of 19.53% under ambient-air processing, outperforming the 1,8-diiodooctane (DIO)-treated device with a PCE of 17.30%. Notably, the devices still delivered a high PCE of 18.30% at an active-layer thickness of 300 nm, indicating excellent thickness tolerance. The encapsulated DCIB-treated devices retained 95% of their initial efficiency after 300 h of continuous illumination under ambient air, whereas the DIO-treated devices retained only 35%. As a preliminary assessment of scalability, an unoptimized 120 cm² module fabricated in air achieved a PCE of 11.60%. DCIB also demonstrated good universality, enabling D18:L8-BO-based devices to achieve a PCE of 20.32% under ambient air. These results demonstrate that DCIB is an effective solid additive for realizing high-performance thick-film OSCs under ambient-air processing.